TY - JOUR

T1 - Abiotic Conversion of Extracellular NH2OH Contributes to N2O Emission during Ammonia Oxidation

AU - Liu, Shurong

AU - Han, Ping

AU - Hink, Linda

AU - Prosser, James I

AU - Wagner, Michael

AU - Brüggemann, Nicolas

N1 - Funding information: The authors wish to thank Holger Wissel for his assistance with 15N isotope analysis, Franz Leistner for his assistance in gas chromatography and Kerim Dimitri Kits for helpful discussions. We would like to thank Andreas Pommerening-Röser (University of Hamburg, Germany) for providing us with AOB strains, and Maria Mooshammer and Ma? ton Palatinszky for their assistance in cultivating Nitrososphaera viennensis and Ca. Nitrosotenuis uzonensis, respectively. S.L. was supported by the Chinese Scholarship Council (scholarship no. 201206760007). M.W. and P.H. were supported by an ERC Advanced Grant (NITRICARE, 294343). L.H. is funded through the Nitrous Oxide Research Alliance (NORA), a Marie Sk?odowska-Curie ITN and research project under the EU’s seventh framework program (FP7).

PY - 2017/11/21

Y1 - 2017/11/21

N2 - Abiotic processes involving the reactive ammonia-oxidation intermediates nitric oxide (NO) or hydroxylamine (NH2OH) for N2O production have been indicated recently. The latter process would require the availability of substantial amounts of free NH2OH for chemical reactions during ammonia (NH3) oxidation, but little is known about extracellular NH2OH formation by the different clades of ammonia-oxidizing microbes. Here we determined extracellular NH2OH concentrations in culture media of several ammonia-oxidizing bacteria (AOB) and archaea (AOA), as well as one complete ammonia oxidizer (comammox) enrichment (Ca. Nitrospira inopinata) during incubation under standard cultivation conditions. NH2OH was measurable in the incubation media of Nitrosomonas europaea, Nitrosospira multiformis, Nitrososphaera gargensis, and Ca. Nitrosotenuis uzonensis, but not in media of the other tested AOB and AOA. NH2OH was also formed by the comammox enrichment during NH3 oxidation. This enrichment exhibited the largest NH2OH:final product ratio (1.92%), followed by N. multiformis (0.56%) and N. gargensis (0.46%). The maximum proportions of NH4+ converted to N2O via extracellular NH2OH during incubation, estimated on the basis of NH2OH abiotic conversion rates, were 0.12%, 0.08%, and 0.14% for AOB, AOA, and Ca. Nitrospira inopinata, respectively, and were consistent with published NH4+:N2O conversion ratios for AOB and AOA.

AB - Abiotic processes involving the reactive ammonia-oxidation intermediates nitric oxide (NO) or hydroxylamine (NH2OH) for N2O production have been indicated recently. The latter process would require the availability of substantial amounts of free NH2OH for chemical reactions during ammonia (NH3) oxidation, but little is known about extracellular NH2OH formation by the different clades of ammonia-oxidizing microbes. Here we determined extracellular NH2OH concentrations in culture media of several ammonia-oxidizing bacteria (AOB) and archaea (AOA), as well as one complete ammonia oxidizer (comammox) enrichment (Ca. Nitrospira inopinata) during incubation under standard cultivation conditions. NH2OH was measurable in the incubation media of Nitrosomonas europaea, Nitrosospira multiformis, Nitrososphaera gargensis, and Ca. Nitrosotenuis uzonensis, but not in media of the other tested AOB and AOA. NH2OH was also formed by the comammox enrichment during NH3 oxidation. This enrichment exhibited the largest NH2OH:final product ratio (1.92%), followed by N. multiformis (0.56%) and N. gargensis (0.46%). The maximum proportions of NH4+ converted to N2O via extracellular NH2OH during incubation, estimated on the basis of NH2OH abiotic conversion rates, were 0.12%, 0.08%, and 0.14% for AOB, AOA, and Ca. Nitrospira inopinata, respectively, and were consistent with published NH4+:N2O conversion ratios for AOB and AOA.

KW - Ammonia

KW - Archaea

KW - Nitrification

KW - Nitrosomonas europaea

KW - Nitrous Oxide

KW - Oxidation-Reduction

KW - Phylogeny

KW - Soil Microbiology

UR - http://www.scopus.com/inward/record.url?scp=85035341035&partnerID=8YFLogxK

U2 - 10.1021/acs.est.7b02360

DO - 10.1021/acs.est.7b02360

M3 - Article

C2 - 29039187

VL - 51

SP - 13122

EP - 13132

JO - Environmental Science & Technology

JF - Environmental Science & Technology

SN - 0013-936X

IS - 22

ER -